This invention relates to a noise suppression device, and more particularly to a device effective for suppressing generation of noise from a circuit by externally fitting it on a line in semiconductor circuits; such as switching electric source circuits, or other sorts of devices such as rectifiers and capacitors.
Semiconductor circuits, as exemplified by switching electric source circuits, that control a large electric current in a high frequency region have for a long time had the problem that a current spike or ringing tends to be produced owing to the properties of semiconductors themselves or other factors in the circuits. There is a possibility that these phenomena impede normal operation of circuits, finally resulting in destruction of the semiconductors themselves.
Moreover, the above abrupt changes that occurred in circuits during switching operation may generate conduction noise and radiation noise to bring about noise problems in the equipment in which the circuits are incorporated.
In recent years, international demands for taking stronger countermeasures to such noise problems have strongly promoted efforts to prevent generation of noise in the equipment in which semiconductor circuits are incorporated.
As one of such countermeasures, it has been practiced, for example, to externally fit a small inductor, called a ferrite bead, on a lead of the rectifiers to be incorporated in semiconductor circuits. The ferrite bead used here is obtained by molding ferrite powder into a toroidal shape, followed by sintering.
This noise suppression device, however, is affected by the properties inherent in the ferrite itself that constitutes the device so that it has such a small rectangular ratio (Br/B.sub.1 where Br is residual flux density and B.sub.1 is flux density) and saturated magnetic flux density that it can achieve only a small noise-suppressing effect. It hence becomes necessary to make it larger in order to make effective use thereof. In this device, it may also occur that the self-loss of ferrite at the time of operation brings about such a sudden heat build-up in the inner diameter side of a hollow center through which the lead of rectifiers is inserted that a great temperature difference is produced between it and the outer diameter side. Because of the poor thermal conductivity and heat-dissipation property of the ferrite, this temperature difference may also cause generation of thermal stress in the ferrite bead. Such stress may frequently bring about the situation that the ferrite bead is broken. In other words, the ferrite bead can not endure long-term use.
In addition, in the instance where this ferrite bead is used in combination with an inductor of rectifiers or a capacitor and a inductor, the ferrite, which has a high electrical resistance and a small magnetic shielding effect, can not be said to have a sufficient performance in regard to suppression of conduction noise and radiation noise, and thus can not be satisfactory for practical use in regard to its reliability.
Taking account of these factors, recently developed is a noise suppression device employing a ribbon of an amorphous magnetic alloy.
This device comprises a toroidal core formed by winding an amorphous magnetic alloy ribbon with a given ribbon width to produce a hollow center with a given inner diameter, coating the whole with a resin such as epoxy resin, and thereafter applying the winding of wire with given turns to the part on which the ribbon has been wound, and may include devices commercially available under trade names of, for example, "SPIKE KILLER" (produced by Toshiba Corporation).
The above noise suppression device employing the amorphous magnetic alloy ribbon may suffer less breaking troubles in use, is feasible for long-term use, and is superior in the noise suppression performance, but has the following problems in practical use, that must be solved.
First, it can not be provided by incorporating devices in series in a semiconductor device itself, and, with respect to a printed circuit board prepared after a circuit has been once formed, it also can not be directly incorporated in its circuit, causing the problem that the printed circuit board must be made over. Further, because of its relatively large size in terms of shape and dimension, it has a problem in regard to a need for space saving, and requires a somewhat complicated process in that in its preparation the winding of wire with given turns is applied to the part on which the ribbon has been wound, of the core formed in a toroidal shape, by winding the ribbon.